The invention relates to a premounted (preassembled) contact-making unit having a screw which has a head and a shank, and a holding unit.
In addition, the present invention relates to a holding unit for such a contact-making unit, and to a method for attaching at least one connection part to a workpiece, and a screwing tool for carrying out this attachment method.
Generally, the present invention is concerned with the field of what are referred to as earthing bolts (grounding studs), such as are often used in particular in motor vehicle engineering. In order to establish a stable earthing contact, a bolt or a nut is welded onto a piece of sheet metal of a vehicle bodywork so that the bolt or the nut is connected to the piece of sheet metal in an electrically conductive fashion. A connection part such as a cable lug is then connected electrically to the bolt or to the nut by screwing a nut onto the bolt or screwing a screw into the nut. In this context it is generally problematic that a surface coating process takes place between the welding on of the bolt (nut) and the securing of the connection part (cable lug). In order to keep the contact faces for the establishment of an electrical connection free of surface coating, it is known to cover these contact sections. The covering parts which are used for this are discarded here before the connection part is secured. The document EP 0 641 944 A1 discloses using as a covering part a nut which is subsequently also used again to attach the connection part. For this reason it is not necessary to discard a part. However, the mounting process overall is somewhat more complex.
German patent application 10 2006 056065.5 forms a prior art according to paragraph 3(2) of the German patent law.
From this application it is known to weld a bolt with an axial blind hole onto a piece of sheet metal. In this context, the blind hole bolt has, in the blind hole, a first threaded section which is covered by a covering part (in particular a plug which is relatively short and is inserted into the blind hole from above). A cable lug is threaded onto a screw with a second threaded section and the screw is screwed into the blind hole. In this context, the plug is also pressed downwards onto the bottom of the blind hole. Of the two threaded sections, at least one threaded section can be embodied as a self-tapping threaded section. Accordingly, in this context electrical contact is established between the cable lug and the underside of a head of the screw, and via the self-tapping threaded engagement between the screw and the blind hole bolt and consequently with the piece of sheet metal onto which the blind hole bolt is welded.
In this context, it is also known from the aforesaid German patent application to insert at least one cable lug in the radial direction into a holding unit and then introduce a screw into the holding unit. In this context, the shank of the screw penetrates the hole in the cable lug, and latching means engage behind the head of the screw. Consequently, a pre-mounted attachment arrangement is provided which has the holding part, the screw and at least one cable lug which is threaded onto the screw. Since the screw penetrates the hole in the cable lug, the cable lug is pre-vented from being pulled out radially from the holding unit. In addition, there may be further latching means present in order to prevent the screw from dropping out of the holding part. In one particular embodiment, apart from radial holes for laterally introducing cable lugs it is also possible to provide, in the case of one holding part, that a further cable lug is pressed from below in the axial direction into the holding device onto the pre-mounted attachment arrangement, composed of the holding part, the screw and the at least one cable lug. This particular embodiment can, as a result, be used as follows. The premounted attachment arrangement set out above can be premounted on a cable lug. In this context, it is possible, for example, for one or more cable lugs to be inserted laterally into the holding unit and subsequently guided by the screw in order to hold both the screw and the cable lugs on the holding unit in a captive fashion. When the cable harness is mounted, it is then possible subsequently to insert one or more further cable lugs from below, that is to say in the longitudinal direction, into the holding part locally and push them onto the screw before the screw is screwed into a blind hole bolt (earthing bolt) described above.
Against the background above, an aspect of the invention is to specify an improved system for implementing an earthing connection and arrangements and methods which can be used for this purpose.
According to an aspect of the invention, a premounted (preassembled) contact-making unit having a screw which has a head and a shank, and a holding unit, wherein the holding unit has a connection part-holding section into which at least one connection part can be inserted, and a screw-holding section into which the screw is inserted in the longitudinal direction in such a way that the screw is held therein captively in the longitudinal direction but in a rotatable fashion, and in that a connection part which is inserted into the connection part-holding section can make electrical contact with the inserted screw, wherein a radially protruding bearing section is formed on the head, and the screw-holding section has a shoulder section by means of which the bearing section is supported axially on the holding unit.
With the premounted contact-making unit it is possible to prefabricate a holding unit and a screw. Since the screw, the holding unit and the blind hole bolt are preferably manufactured by the same manufacturer, the screw can here be coordinated with a blind hole bolt, in particular in the case of an embodiment with a self-tapping thread. The premounted contact-making unit can be used during the manufacture of a cable harness to insert connection parts, for example cable lugs, into the connection holding section.
Also according to the above aspect, a premounted contact-making unit, having an annular section and a plurality of longitudinal webs which extend in the longitudinal direction from one side of the annular section, wherein a shoulder section on which a bearing section of a screw can be axially supported is formed on the inner circumference of the annular section, said bearing section being formed on the outer circumference of a head of the screw, wherein in addition first latching means which are configured so as to engage behind the bearing section from the other axial side are formed on the inner circumference of the annular section, wherein at least one connection part can be inserted between the plurality of longitudinal webs in such a way that a connection section of the connection part extends in the radial direction between two longitudinal webs, wherein second latching means which are configured so as to hold an inserted connection part in a captive fashion are formed on the longitudinal webs.
As a result of the measure of providing, on the inner circumference of the annular section, first latching means which are configured to engage behind the bearing section or another part of the screw from the other axial side, the screw can be correctly positioned in the holding section. In other words, the screw can be positioned aligned precisely in the longitudinal direction in the holding part. Owing to this optimized centring of the screw, connection parts can easily be inserted into the holding part. The centring also permits facilitated screwing into a blind hole bolt or the like. Since the centring is preferably carried out by means of the bearing section on the outer circumference of the head, the latter advantageously has no influence on a contact surface on the underside of the head.
The above aspect is also achieved by a method for attaching at least one connection part on a workpiece, having the steps: a) provision of a premounted contact-making unit which has a first attachment element and a holding unit on which the first attachment element is held in a captive fashion, b) insertion of the at least one connection part into the holding unit, wherein the connection part makes contact with the first attachment element, and connection of the first attachment element to a second attachment element which is secured to the workpiece.
The manufacture of an earthing contact can easily be implemented in this way with a small number of steps. Providing the pre-mounted contact-making unit makes it possible to plug on in each case one or more connection parts (such as cable lugs) at a cable harness manufacturer and/or during the mounting of the cable harness (for example on a vehicle bodywork), and the screw can subsequently be easily secured, by virtue of its correct positioning, in a second attachment element (such as for example the blind hole or the bolt) which has been attached to the workpiece in advance. No connection parts are preferably secured to the premounted contact unit before step b).
In addition, according to an aspect of the invention it is possible to monitor the connection process in an attachment method for connecting a first attachment element to a second attachment element by means of a self-tapping threaded engagement, by virtue of the fact that the torque which is applied during the connecting process is measured over time and/or the rotational angle.
Since, in the case of a self-tapping threaded engagement, there is an increased demand for torque from the start of the threaded engagement and said demand can be measured, it is possible, for example, to sense the rotational angle or the number of rotations of the first attachment element with respect to the second attachment element. As a result, the connection process can be monitored.
Finally, the above may be achieved by a screwing tool for carrying out the above-described attachment method, having a tool section which is configured so as to engage on a tool engagement portion which is provided on a head of the first attachment element in order to apply torque to the head, and having an anti-rotation device which is configured so as to prevent rotation of the at least one connection part, while the first attachment element is screwed onto the second attachment element.
With this type of screwing tool it is consequently possible to ensure that a cable set which is connected to the connection parts cannot rotate.
With the previously mentioned, premounted contact-making unit it is preferred if the screw-holding section has first latching means which engage radially behind the bearing section so that the screw is held captively in the longitudinal direction in the holding unit.
In this way it is possible to ensure that the screw does not become detached from the holding unit.
The bearing section, the shoulder section and the first latching means may be embodied in such a way that the screw is aligned axially in the holding unit, in particular is held centred in the longitudinal direction, in which case the advantages described above can be achieved.
The bearing section and/or the shoulder section may be embodied in a stepped fashion.
The bearing section can be embodied here, for example, as a flange section (collar) which protrudes radially from the head of the screw.
As an alternative to this it is possible to make the bearing section and/or the shoulder section conical in design.
In this embodiment the screw can be embodied as a counter sunk head screw.
Overall it is also preferred if the screw is held completely within the holding unit.
In other words it is possible to ensure that the screw is completely surrounded by the holding unit. This is advantageous in particular if the screw is manufactured from metal and if the holding unit is manufactured from plastic. It is possible to ensure here that the screw does not cause any damage to other parts (bodywork of a vehicle) during transportation or mounting.
According to another embodiment, the connection part-holding section has second latching means in order to hold the at least one connection part, to be inserted therein, in a captive fashion in the longitudinal direction.
There is in particular provision here that a connection part that is inserted into the holding section is held in the axial direction by the head of the screw. Measures may be taken so that a connection part which is inserted first into the holding unit can make contact electrically with the underside of the head of the screw reliably and over a large area. In the other axial direction, the second latching means serve to prevent the connection part from dropping out of the holding unit.
Although latching means may be provided both for the screw and for the connection parts in order to hold the screw or connection parts on the holding unit in a captive fashion, it is generally also conceivable to provide clamping means or the like instead of the latching means.
The connection part-holding section may also have for a connection part which is to be inserted therein, a radial recess through which a connection section of the connection part can extend outwards in the radial direction.
In particular when a plurality of such radial recesses which are arranged distributed over the circumference of the holding part are formed, it is possible as a result to ensure that the cable lugs cannot slide one over the other when the screw is screwed tight onto a blind hole bolt or the like.
In addition, the sections of the connection part which extend between the radial recesses can be used to support the second latching means in order to hold the connection parts in a captive fashion.
The radial recess may extend in the longitudinal direction from one end of the holding unit.
In this embodiment it is possible to introduce the connection parts into the holding unit exclusively in the axial direction. This makes it possible to insert connection parts successively into the holding unit at different locations, that is to say for example when the cable harness is manufactured, when the cable harness is mounted, in the case of repair work and/or when electric accessories (for example subsequent installation of a radio or navigation device) are mounted and when a further cable lug for forming an earth contact is used, as is possibly necessary in this context.
According to another embodiment, the connection part-holding section is embodied in such a way that a plurality of connection parts can be held therein, wherein the connection parts can be inserted into the connection part-holding section exclusively in one direction which is opposed to the direction in which the screw is inserted into the screw-holding section.
This embodiment of the premounted contact-making unit is also considered to be a separate invention, independently of the formation of a bearing section or of a shoulder section.
Since the situation is avoided in which connection parts are inserted radially or laterally into a holding part, it is possible to enable the premounted contact-making unit to be manufactured exclusively from the screw and the holding unit, wherein the connection parts (cable shoes) can all be introduced subsequently into the premounted contact-making unit.
In addition it is advantageous if the holding unit has, on the outer circumference, an anti-rotation section on which an anti-rotation device of a tool, by means of which the screw can be screwed to an attachment element, can engage.
In this context as a result of the engagement of the anti-rotation device of the tool on the anti-rotation section the cable set is prevented from being able to rotate when the screw is screwed on to an attachment element (blind hole bolt). The anti-rotation device on the tool can be made relatively small. In addition, an anti-rotation means can be implemented independently of the geometry of the connection parts.
In the case of the attachment method which is used for monitoring it is particularly preferred if the start of the threaded engagement is sensed by sensing the torque requirement which is increased by the self-tapping threaded engagement, and if the rotational angle or the number of rotations is sensed from the start of the threaded engagement up to the tightening of the threaded connection.
As a result it is possible to monitor the entire connection or screwing process.
This makes it possible to determine whether a correct number of connection parts has been inserted between the first and the second attachment elements (since given a different number of connection parts there are also different rotational angles or revolutions until the threaded connection is tightened).
It may also be advantageous if the measured torque curve is compared with at least one target curve or envelope curve which is specified for a predefined number of connection parts to be secured and/or for a predefined length of threaded engagement.
In the case of the screwing tool according to the invention, the anti-rotation device may be configured so as to engage on an anti-rotation section of the holding unit. The anti-rotation device can be made compact here, in particular in the longitudinal direction.
According to another embodiment, the anti-rotation device is configured so as to engage on at least one connection section, protruding radially from the holding unit, of the at least one connection part.
This embodiment also ensures that the cable set cannot rotate when the screw is screwed tight in the blind hole bolt. In this context, the connection parts themselves are prevented from rotating. In other words, the connection sections of the connection parts abut against the anti-rotation device so that damage to the holding unit (preferably manufactured from plastic) is avoided. The connection sections of the connection parts are preferably formed by metallic sections.
The screwing tool may have a tubular mouthpiece into which the holding unit can be introduced.
In particular it is possible as a result to insert the entire pre-mounted contact-making unit, including the connection parts which have been introduced into it, into the mouthpiece in order subsequently to screw the screw into the corresponding attachment element (for example blind hole bolt) by means of the screwing tool.
A holding device may be formed on the mouthpiece in order to hold the holding unit on the mouthpiece. The holding device can be a clamping holding device or a latching holding device.
In addition, the anti-rotation device may be formed on the mouthpiece.
As a result, the mouthpiece can not only fulfil the function of holding the premounted contact-making unit but can also fulfil the function of preventing rotation of the cable set during the screwing-on process.
According to the various embodiments and aspects of the invention it is possible to achieve various results, such as:
The bearing section can prevent the screw from slipping out of the holding unit. When the first latching means is used, the screw can be held in the holding unit in a captive fashion in both longitudinal directions.
It is possible to ensure that the screw is held centrally in the holding unit solely by means of the head so that the shank is exposed. The underside of the head (the contact face for the connection parts) can also be kept completely free here.
The screw can, for example, be manufactured economically as an extruded part without subsequent working.
The holding part makes it possible to expose the underside of an inserted connection part and to insert an attachment element such as a blind hole bolt into the holding unit in order to make contact with the underside of a connection part.
The connection parts can, for example, be fitted by a cable harness manufacturer, but it is also possible to insert them subsequently when the cable harness is mounted, without removing the contact-making unit. Subsequent insertion of connection parts in a workshop is possible without removing the contact-making unit.
The closed design of the holding unit makes it possible to easily position it correctly in a mouthpiece of the screwing tool.
In addition, the holding unit can be manufactured from plastic, for example by means of an injection moulding tool without a slide.
Compared to known solutions in which a nut or some other part on the outside of the threaded bolt serves as a surface coating protection, a series of further advantages can be achieved, such as are described in particular in the German patent application 10 2006 056 065.5 mentioned above. Reference is made here to its disclosure contents. The disclosure of this application is to be considered as being included in the scope of the present application through reference.
When the cable harness is mounted, it is not possible for any part to be lost since they are either fixedly mounted on the bodywork or on the cable set (of the contact-making unit).
In particular a blind hole bolt of the type described above can be used as an attachment element into which the screw can be screwed. In this context, a standard weld head can be used. Using such a welded bolt avoids holes in the piece of sheet metal (sound bridges and penetration of moisture are avoided). There is no disruptive surface coating in the contact area.
Since the connection parts (cable lugs) are accommodated in the holding unit before the mounting process, it is possible to prevent the connection parts from scratching the surface coating of the bodywork of a vehicle or the like.
Finally it is possible to ensure that a connection part seals off a non-corrosion-protected area in the interior of a blind hole bolt from the outside.
The premounted contact-making unit described above and the corresponding attachment methods for this purpose can ideally be implemented in conjunction with a hollow bolt which is welded to a piece of sheet metal by means of a conventional bolt (stud) welding process, for example. Such a hollow bolt has on the inner circumference an inner thread, preferably an inner section which can be tapped by a screw with a self-tapping thread. In addition, it is particularly preferred if this hollow bolt is closed off with a plug, preferably composed of plastic, after said hollow bolt has been welded on to the workpiece or piece of sheet metal. This can prevent the inner section being coated with an insulating layer during a subsequent surface-coating process or the like. When the screw is screwed into the inner section, the plug can then be pressed downward onto the bottom of the hole of the hollow bolt and remain there.
With such a hollow bolt it is possible, according to a further aspect of the invention, to use an attachment arrangement which serves to attach a hose line to a workpiece such as a piece of sheet metal, in which case the outer circumference of the hose line is electrically conductive and the attachment arrangement has a line holder made of an electrically conductive plastic and screw whose head engages behind the line holder and which can be screwed into such a hollow bolt which is secured to the workpiece.
Such an attachment arrangement can be used in particular to attach petrol lines or the like to the bodywork of a vehicle, in which case static charges can be particularly satisfactorily diverted via this attachment arrangement. Electrical contact can be implemented over a large area by means of the connection between the screw and the hollow bolt (the threaded engagement) and static charges on the hose line can be reliably diverted via said electrical contact.
It is particularly preferred here if the hollow section of the hollow bolt is closed off with a plug which can be pressed into the hollow section, before the screw is screwed into the hollow bolt.
It is also preferred for the line holder to have a receptacle section into which the head of the screw can be clipped in a captive fashion in order to form a premounted contact-making unit.
The line holder can also have receptacle sections for clipping in one or more hose lines. Instead of hose lines, it is also possible to use other lines which are embodied in an electrically conductive form on the outer circumference.
In the present context, the screw is to be understood as referring generally to a component which has a threaded shank and a head. The threaded shank can be here a shank with an outer threaded section or a hollow shank having an inner threaded section. A threaded section can be a section with a self-tapping thread or else a tappable section into which a thread can be tapped by means of a complementary component with a self-tapping thread. The term self-tapping thread is intended to encompass all types of self-tapping, self-cutting threads etc.
Of course, the above-mentioned features, which are also explained below, can be used not only in the respectively specified combination but also in other combinations or alone without parting from the scope of the present invention.